I need to modify a chuck's jaws so they can handle high temperatures, but will not scratch the workpiece. (Glass). The load will be very small.
I will probably use aluminium jaws and either coat them with, or attach to them, this material.
Example items being held:
- Borosilicate glass tube, 30mm long, 6mm diameter, 5g weight
- Borosilicate glass tube, 50mm long, 30mm diameter, 50g weight
The tube will be held horizontally by the chuck, and should be supported such that the other end will not droop by more than 2mm. That end is held in a propane bunsen flame, on the edge of the hottest part of the flame: a cone 15-20mm height, with a base ~12mm, 1200-1400°c.
I do not have figures on what the chuck jaws will have to withstand, but the air passing over the tip of the jaws probably wouldn't be more than about 250°c, and the temperature of the glass at that point will be about the same.
Of issue might be the heat radiated from the flame - so a heat reflecting material will help.
Also, since the rest of the chuck will be barely above room temperature, it may help to have thermally conductive material to dissipate heat from the tips of the jaws to the chuck.
Plastics seemail like an obvious choice for softness, but high temperature plastics seem hard to find. Silicone (260°c) and PTFE (204°c) are barely temperature resistant enough, but so far seem like the best choice, since higher temperature polymers like Vespel (300-400°c) are very hard to come by.
What alternatives are there? Metals? Composites?
The only other approach I might use is a heat shield directly in front of the chuck, but it would be awkward, as it would have to fit quite snugly around the workpiece, different shields would be needed for different size workpieces, and would be time consuming if batches of workpieces need to be processed. I can't imagine how this could be automated for large batches. Even then, scratching the workpiece could be a problem.